The present invention relates to vehicle wheels and tires and in particular to such wheels and tires used in off-highway vehicles.
It is of course well known to provide a vehicle with a pneumatic tire mounted upon a wheel rim to support the mass of the vehicle. With off-road vehicles, such as construction equipment or material handling equipment, it is usual to use relatively large diameter wheels and large aspect ratios; that is, the ratio of the height of the tire to the width of the tire, to support the high loads normally encountered. In this manner, the tire may deflect to present a footprint capable of supporting the loads on the vehicle.
One problem associated with such combinations of wheels and tires is the instability introduced at higher speeds, particularly during travel along paved highways. In those situations, the flexibility found in conventional tire construction causes bouncing of the tire and renders control of the vehicle difficult.
In order to be commercially viable, it is necessary to be able to mount the tire to a one-piece rim using conventional tire installation equipment. For this purpose, a well is provided in the central portion of the rim to accommodate a bead seat and allow the tire to be fed over the rim prior to inflation. To seal the tire against the rim, a bead seat is provided and to be effective this must ensure an adequate interference between the tire and the wheel to effect a seal. Typically the bead seat is formed with an inclination to the axis of rotation in the order of 5xc2x0. While this facilitates ease of installation, it does not effectively seal the tire particularly under the high lateral loads that may be encountered during normal use. An alternative configuration in general use has a 15xc2x0 bead seat. This configuration is derived from a three-piece wheel in which tire mounting is facilitated. However, with a single piece wheel, a 15xc2x0 bead seat angle is difficult to mount and does not offer good retention.
It is therefore an object of the present invention to provide the components of a vehicle wheel assembly that obviate or mitigate the above disadvantages.
In general terms, the present invention provides a tire for a vehicle that has a pair of annular beads laterally spaced apart along the axis of rotation. A plurality of plies extend between the beads to define a tire having a pair of radially extending sidewalls and a tread portion. An elastomeric cap covers the carcass and extends across each of the sidewalls and the tread portion. The plies extend about the beads to provide an inwardly directly bead seat for sealing against a rim. The bead seat has a substantially frustoconical inwardly directed sealing surface inclined to the axis of rotation at an angle of between 10xc2x0 and 12xc2x0. The tire has a radial spacing between the sealing surface and the radially outer surface of the cap that is less than or equal to 65% of the maximum width of the tire in a free body state.
In a further aspect of the invention, there is provided a wheel rim for a vehicle. The rim has a circumferential well with a base and a pair of upstanding sidewalls. A pair of lateral extensions project from respective ones of the sidewalls to a pair of bead support surfaces. Each of the bead support surfaces is frustoconical with an included angle of between 20xc2x0 and 24xc2x0. The bead support surfaces terminate at laterally outer edges in upstanding flanges directed to an opposite side of the lateral extensions to the well.
A still further aspect of the invention provides a vehicle wheel assembly having a rim and a tire mounted on the rim. The rim has a centrally disposed well and a frustoconical bead support surface to either side. The bead support surfaces have an angle of between 10xc2x0 and 12xc2x0 with respect to the axis of rotation. The bead support surfaces terminate in an upstanding flange overlapping a radially inner portion of the tire. The tire includes a pair of annular beads, each associated with a respective one of the bead seats. A plurality of plies extends between the beads to define a tire having a pair of radially extending sidewalls and a tread portion. An elastomeric cap covers the tire and extends across each of the sidewalls and the tread portion. The plies extend about the beads to provide an inwardly directed bead seat for engagement with the bead support surfaces. The bead seat has a substantially frustoconical inwardly directed sealing surface complementary to the bead support surfaces. The tire has a radial spacing between the sealing surface and a radially outer surface of the cap that is less than or equal to 65% of a maximum width of the tire in a free body state.